Quantum nucleation in a single-chain magnet.

The field sweep rate (upsilon = dH/dt) and temperature (T) dependence of the magnetization reversal of a single-chain magnet is studied at low temperatures. As expected for a thermally activated process, the nucleation field (H(n)) increases with decreasing T and increasing upsilon. The set of H(n)(T,upsilon) data is analyzed with a model of thermally activated nucleation of magnetization reversal. Below 1 K, H(n) becomes temperature independent but remains strongly sweep rate dependent. In this temperature range, the reversal of the magnetization is induced by a quantum nucleation of a domain wall that then propagates due to the applied field.